1. Field of the Invention
The present invention relates to a linear actuator for beds or chairs.
2. The Prior Art
Such actuators are by now well-known for beds with an adjustable upper body and leg section, and have developed into an actual low-cost product for the home bed market. However the actuators are also in a more sophisticated version used in care beds. As examples of such type of actuators could be referred to U.S. Pat. No. 5,075,911 Dewert, U.S. Pat. No. 6,300,732 B1 Compact S.r.l., DE 100 47 037 C1. In said actuators there is a drive in each end driven by their own motor. In the example WO 2005/122840 A1, Linak there is only one motor. An example for operating one section only is shown in DE 20 2004 007 549 U1 Dewert. The housing is typically constructed as two plastic shells, and the various components are mounted in one of the plastic shells and the other is screwed onto this with a considerable number of screws. The housing is relatively heavy loaded particularly in the area around the shaft aperture. In order to create sufficient strength it is a requirement that both plastic shells jointly operate as a strength element, hence the many screws. It is not unusual to use more than twenty screws. During the assembly process it is difficult with so many screws, which even need to be screwed in with precision. Moreover the large number of screws should also be taken into consideration when designing the plastic shells, which again complicates the mould tools and the moulding itself.
The object of the invention is to provide an actuator, which complies with the outlined assembly problem and at the same time does not render the actuator more expensive.